Process of gas plating an article with light metal



July 15, 1958 F. E. DRUMMOND 2,843,506

PROCESS OF GAS PLATING AN ARTICLE WITH LIGHT METAL Filed July 13, 1955 U 2 Sheets-Sheet 1 MIX LIGHT METAL SCRAP, TURN/N65, OR POWDER WITH LIOU/D MERCURY HEAT TO FORM AN AMALGAM DECOMPOSE THE AMALGAM INTO A POROUS MASS OF LIGHT METAL AND MERCURY VAPORS HEAT THE POROUS MASS WITH IOD/DE VAPOR TO PRODUCE AN IOD/DE OF THE LIGHT METAL CONTACT THE METAL IOD/DE WITH AN ARTICLE HEATED TO A TEMPERATURE TO DECOMPOSE THE METAL IOD/DE ARTICLE HAVING COATING OF LIGHT METAL IN V EN T 0R.

FOL SOM E DRUMMOND BY /M....;/w....

Attorneys y 1958 F. E. DRUMMOND 2,843,506

PROCESS OF GAS PLATING AN ARTICLE WITH LIGHT METAL Filed July 15, 1955 2 Sheets-Shet 2 IN V EN TOR. F OLSOM E. DRUMMOND BY r United States Patent PROCESS OF GAS PLATIN G AN ARTICLE WITH LIGHT METAL Folsom E. Drummond, Washington, D. C., assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Application July 13, 1955, Serial No. 521,922

4 Claims. (Cl. 117-107) This invention relates to gas plating of light metals such as aluminum, magnesium or the like, and to composite metal bodies produced thereby.

Attempts to produce coatings of light metals such as aluminum and magnesium have been diflicult and of little value commercially because of the necessity of volatilizing the metals. Aluminum metal vaporizes at atemperature of 1800" C. (3272 F.) and magnesium at lllO" C. (2030 F.). The high temperature requirements for volatilizing these light metals, together with the difiiculty of handling such hot metal vapors, and their avid reaction tendency with oxygen and hydrogen at such high temperatures, has greatly mitigated against their use.

In accordance with the present invention, heat-decomposable compounds of these light metals, and which decompose to release the metal at relatively low temperatures, are utilized to deposit by gaseous deposition the light metals. The process of this invention thus overcomes the difiiculties of working with high temperature gases and provides a process for gas plating of light metals, such as aluminum or magnesium.

In accordance with the present invention, aluminum or magnesium metal, or suitable mixtures thereof are deposited directly upon a substratum such as steel, iron, copper, magnesium, aluminum or alloy metals or other and nonmetal materials, e. g., glass, molded plastics, wood and the like. In this manner, the substratum material is provided with a tenaciously bonded metal layer or coating of aluminum or magnesium metal. The process permits gas plating of such light metals at relatively low temperatures as compared to the temperature of the volatilized metals and wherein the metal is deposited directly on the substratum without need of utilizing an inter mediate bonding layer.

The principal object of the present invention is to gas plate such light metals as aluminum or magnesium directly onto a supporting or base surface which may comprise a ferrous or non-ferrous metal or alloy whereby the metal base is provided with an outer shell or layer of substantially pure aluminum or magnesium metal.

Another object of the invention is to provide a composite metal article consisting of a substratum of light metal, such as magnesium or a heavy metal such as iron, and an outer coating or layer of aluminum metal.

Another object of the invention is to provide a composite metal article of the character described, which comprises a gas plated layer of aluminum metal or magnesium metal.

Another object of the invention is to provide a method whereby light metal, such as magnesium and aluminum, may be plated onto metal castings, sheets, strips or the like and fabricated into a wide variety of products and shapes, and where it is desirous that the article have an outer portion composed of light metal.

Another object of the invention is to provide a method whereby metals such as steel, iron, copper and the like "ice may be suitably protected with a layer of aluminum metal, the same being deposited directly onto the substratum.

Another object of the invention is to provide a method of tenaciously uniting aluminum or magnesium metal to a supporting base metal without the necessity of employing an intermediate bonding layer or alloy as has been the practice heretofore.

Another object of the invention is to provide an improved method of gaseous metal plating the light metals of group II and group ill of the periodic system onto the surface of articles.

Another object of this invention is to provide an improved process for plating light metals, such as aluminum and/or magnesium, or other light metals of group II and group III in the periodic system, and wherein amalgams are used in the gas plating of these light metals.

Another object of the invention is to gas plate -aluminum and magnesium onto surface wherein amalgams are utilized in situ to form the heat-decomposable light metal compound which decomposes to deposit the metal under conditions which are commercially feasible.

It is still another object of the invention to provide a method for producing aluminum coated articles whereby aluminum metal is deposited onto the surface of the substratum and into the pores and interstices of the surface to provide an interlocked substantially integral layer or coating of aluminum metal thereon.

These and other objects and advantages will become apparent as the description proceeds.

In accordance with the present invention, articles or materials made of metal or non-metal may be suitably cleaned to remove foreign matter, and are then subjected to gas plating utilizing a heat-decomposable organometallic compound of the light metal, e. g., aluminum or magnesium, or suitable mixtures thereof, to provide a finished composite light metal gas plated product.

Although the invention will be described as applied to the problem of gas plating aluminum or magnesium onto metal surfaces, it will be understood that these nonmetal surfaces are also adapted to be gas plated, if de sired, so long as the substratum is sufiiciently resistant to the temperatures required to effect the gas plating.

In the drawings illustrating the invention,

Figure l is a flow sheet of a preferred method of carrying out the coating process;

Figure 2 illustrates in perspective and in cross-section sheet or strip metal having a coating of aluminum;

Figure 3 is a similar view in perspective as Figure 2, and illustrating strands of metal fabric coated with aluminum metal; and

Figure 4 is a perspective view of a filament or strand made of glass which is provided with an outer coating of aluminum and shown in cross-section.

In gas plating metal surfaces, the metal, after being cleaned of foreign matter, is subjected to gas plating utilizing suitable organo-metallic compounds of aluminum or magnesium, the light metal compounds employed preferably being heat-decomposable at temperatures substantially below the vaporization point of the light metals. The decomposition or dissociation of the compound is made to take place in an atmosphere which is inert and free of oxygen to bring about deposition of the nascent light metal and without oxidation of the metal during the plating operation.

In carrying out the gaseous metal plating in accordance with the preferred practice, metal scrap, e. g. turnings or powdered metal, is mixed with liquid mercury heated to a temperature of about to C. to form an amalgam. The resultant amalgam is then heated in a closed vessel or chamber out of contact with air or oxygen to a temperature of between about 350 and 500 C. to volatilize and decompose the mercury and mercury oxides, leaving a porous mass of substantially pure metal. This heated porous metal residue is reacted with iodine vapors to form the metal iodide which is volatilized in situ and conducted into contact with the article to be plated with light metal, the article being maintained in an atmosphere which is dry and free of air and oxygen and heated to 300 C. or above to cause decomposition of the metal iodide and deposition of the metal constituent on the surface of the article. The resultant plate may be suitably buffed, 'as desired, to produce a finished product. The deposition maybe carried out in an inert gas medium such as helium, argon or nitrogen to prevent oxidation of the light metals. Vacuum conditions may be used, if desired, to speed up the process and eliminate oxygen and reaction of waste gases.

Cleaning. of the metal surface to be plated may be effected by employing mechanical or chemical means, or suitable combinations thereof. Sandblasting, wire brushing, or the like, may be used to remove solid foreign particles. Where the metal surface is to be degreased and cleaned, the same may be washed with petroleum solvents such as xylol, toluene, or the like, and use may be made of aqueous alkaline washes.

A suitable treatment consists of immersing the metal article in a solution containing sodium hydroxide, the temperature of the solution being approximately 100 C. and allowing the metal to soak thereon for from ten to thirty minutes. Thereafter, the article is removed, thoroughly rinsed with clean water and dried at a temperature around 300 C. for a sufiicient time to remove all moisture and provide a thoroughly dry chemically clean metal surface for gas plating with light metal compounds. The thus cleaned metal surface which is retained out of contact with air, and preferably in an inert atmosphere such as nitrogen or helium, is subjected to gaseous metal plating by bringing the same while heated in contact with a heat-decomposable organometallic compound.

As a modification of the process, suitable esters of the metals may be used in place of amalgams to form the porous nascent metal which is reacted with an element to produce a gaseous heat-decomposable compound of the light metal. For example, aluminum acetonate, or esters of lower or higher alcohols such as ethyl, butyl, propyl esters of aluminum or magnesium. These metal compounds decompose at relatively low temperatures when heated in an inert atmosphere, such as helium, argon or the like, to liberate the metal as a porous mass.

The gaseous metal plated material may be heated, if desired, to stabilize the coating, as by heat annealing the plating by subjecting it to a temperature of about ZOO-350 C. for from one to two hours. This annealing step, however, may be omitted where the same is not required, or the use of the article thus plated does not necessitate it.

The following examples are illustrative but not limitative of the process of gas plating light metals:

Example I One hundred pounds of aluminum scrap (turnings) is mixed with 100 pounds of mercury heated to a temperature of about 350 C. to form an amalgam containmg about 0.25 to 0.50% by weight aluminum and which liquid amalgam is drained away from the mass. The resultant liquid amalgam is transferred to a closed vessel or chamber and heated to 4-00-450 C., the vessel or chamber being filled with nitrogen and free *of air or oxygen to volatilize the mercury and decompose the mercury oxides which are drawn off and condensed to recover the mercury, leaving a porous mass of substantially pure aluminum.

While the resultant porous mass of pure aluminum is maintained free "of air and oxygen and heated to about ZOO-250 C., iodine vapor is brought in contact with the heated porous mass to form aluminum iodide which volatilizes, the vapor being conducted to a gas plating chamber where it is circulated into contact with the article to be plated with aluminum metal, the same being maintained in a dry, inert atmosphere of nitrogen. The article is heated to a temperature of 300-350 C. or sufficiently high to cause the aluminum iodide to decompose and deposit aluminum metal, the iodine vapor being drawn away and collected for re-use.

Example II The process of Example I is repeated substituting magnesium scrap or turnings for aluminum to 'form the amalgam which is heatedto dry oil the mercury and mercury oxides and reacted with iodine vapor to form magnesium iodide, the latter being heat-decomposed in contact with the metal article to be plated with magnesium metal.

Example III In this example the process is carried'out as described in Example I .using HCl gas instead of iodine vapor to form aluminum hydrochloride which is conducted in contact with the metal surface or article to be plated with aluminum metal, the article being heated to about 200 C. in nitrogen to cause decomposition of the aluminum chloride and deposition of aluminum metal.

Example IV In this example the process of Example I is repeated while the system is maintained under subatmosphere pressure conditions (15 to 20" Hg) and in an atmosphere of dry nitrogen as the inert carrier for the iodine vapors and to remove volatilized mercury and mercury compounds during formation of the porous pure aluminum metal. The temperatures in this instance are adjusted downward as desired as a result of operating under subatmosphere pressure conditions.

Example V In this example the method is carried out as in Example II using magnesium diethyl as produced in situ which is brought in contact with a dry, clean steel sheet heated to 350 C. in an atmosphere of helium to cause decomposition of the magnesium diethyl and deposition of the metal on the steel surface.

Example VI In this example the method as set forth in Example I is repeated using chlorine gas to treat the heated porous aluminum metal formed during the amalgam treatment, the resultant anhydrous aluminum chloride formed is sublimed and conducted in contact with the metal surface to be plated whereupon the temperature is raised to 600 C. or above to cause dissociation of the aluminum chloride and deposition of the aluminum metal, the dissociation being carried out in a 'cham'berevacuated of air and filled with dry nitrogen.

Light metals such as aluminum and magnesium are thus plated directly onto a substrate metal which may be an alloy metal such as steel, copper, iron, etc. whereby there is produced a composite product comprising the light metal integrally and tenaciously bonded to a metal or metal alloy surface of an article.

In carrying out the method of gas plating light metals, as described, the 'steps of distilling off the mercury and mercury compounds to produce a porous pure metal residue, and the reaction of the same with a substance to produce a heat-decomposable compound, and the contacting of the resultant compound with the heat article to effect the plating are preferably performed together or in situ. Thus, the system is preferably hermetically sealed against the entrance of air or oxygen during formation of the heat-decomposable light metal compound and its circulation or passage in contact with the article which is to receive a coating or deposit of the light metal.

The process is applicable for providing magnesium articles with a protective coating of aluminum. Similarly, magnesium metal coatings may be produced on articles or surfaces.

The thickness of the light metal coatings may be varied by limiting or extending the time the metal-bearing gas is circulated in contact with the heated metal to be plated. A coating of 0.001 to 0.0025 inch is generally adequate for providing protection against corrosion in most instances.

The process makes possible continuous straight-line production of composite magnesium-aluminum products, such as wire, cable, metal plate, strip, sheet material or screen. The thickness of the coating may be controlled by limiting the duration of the gas plating or time the article remains in the plating enclosure. The invention is particularly useful in aluminizing metals where it is desirous that the metal be deposited into the pores and interstices of the base metal surface to form a substantially integral outer shell of aluminum or magnesium metal.

The material being gas plated with the 'light metals may be composed of various metals or alloys and in the various shapes and forms described. To clean the metal preparatory to gas plating, use may be made of conven tional methods, such as washing or immersing the material in alkali or acid solutions, and rinsing with clear hot water and heating to 150-200 C. for sufficient time to drive off all moisture and produce a perfectly dry surface. Electro-chemical cleaning methods as commonly used also may be employed, if desired, as well as mechanical cleaning methods, e. g. Wire brushing and sandblasting.

Pre-heating and drying of the article prior to gas plating is preferably carried out in an inert atmosphere such as nitrogen, helium or the like to prevent oxidation. Thereafter the heated and completely dry metal surface is subjected to gas plating.

By employing gas plating in accordance with this invention, it is possible to envelope the material or article by a metal film or plate of any desired thickness, and which consists of substantially pure metal. A protective film is thus provided which film or plating does not have occluded foreign matter as is inherent in conventional molten metal spray and dipping methods.

Employing amalgams in accordance with this invention provides an economical process and permits as starting materials aluminum or magnesium scrap metal. The mercury dissolves the oxides of the metal and the mercury and mercury oxides and compounds formed are readily volatilized at the temperatures used and the mercury is condensed for use over and over again.

The process produces light metals which are free of oxides and impurities and are porous so that they readily react with the halide or the like to form a compound which is heat-decomposable at relatively low temperatures and which is commercially practical to use.

Gas plating, in accordance with this invention, makes it possible to bring nascent pure metal in direct contact with chemically clean substrate surfaces on which the metal is to be plated, and due to the deposition of the metal from a gaseous state, the penetration of the same deeply into the pores and interstices of the metal is accomplished without the inclusion of impurities and such as will alter the physical characteristics of the metal so that the interstitial plate portions function to actually enhance the physical characteristics of the base metal or substrate.

It will be understood that while there has been described and set forth certain specific embodiments of this invention, it is not intended to be limited thereto and that it is manifest that various substitutions and changes may be made by those skilled in the art, and to which the invention is readily susceptible, and which modifications and changes are intended to come within the scope of this disclosure and as more particularly set forth in the appended claims.

What is claimed is:

1. A process of gas plating an article with light metal utilizing scrap light metal as a starting material, said process comprising the steps of admixing said scrap light metal with mercury and heating the mixture to form an amalgam of the light metal, continuing the heating of said amalgam at a higher temperature and under non-oxidizing atmospheric conditions to volatilize the mercury leaving a porous mass of substantially pure light metal while retained in said atmosphere, thereafter reacting the resultant porous metal under said non-oxidizing atmospheric conditions with a reactant to form a heat-decomposable compound of the light metal, and contacting the article to be plated with said heat-decomposable light metal compound while heated to a temperature sufiicient to decompose said light metal compound and cause deposition of the light metal onto the surface of the article.

2. A process of gas plating an article with aluminum utilizing scrap aluminum metal as a starting material, said process comprising the steps of admixing said scrap aluminum metal'with mercury and heating the mixture to form an amalgam of the aluminum, continuing the heating of said amalgam at a higher temperature and under nonoxidizing atmospheric conditions to volatilize the mercury leaving a porous mass of substantially pure aluminum metal while retained in said atmosphere, threafter reacting the resultant porous metal under said non-oxidizing atmospheric conditions with a reactant to form a heatdecomposable compound of the aluminum metal, and contacting the article to be plated with said heat-decomposable aluminum metal compound while heated to a temperature sufficient to decompose said aluminum metal compound and cause deposition of the aluminum metal onto the surface of the article.

3. A process of gas plating an article with magnesium utilizing scrap magnesium metal as a starting material, said process comprising the steps of admixing said scrap magnesium metal with mercury and heating the mixture to form an amalgam of the magnesium, continuing the heating of said amalgam at a higher temperature and under non-oxidizing atmospheric conditions to volatilize the mercury leaving a porous mass of substantially pure magnesium metal while retained in said atmosphere, thereafter reacting the resultant porous metal under said nonoxidizing atmospheric conditions with a reactant to form a heat-decomposable compound of the magnesium metal, and contacting the article to be plated with said heatdecomposable magnesium metal compound while heated to a temperature sufficient to decompose said magnesium metal compound and cause deposition of the magnesium metal onto the surface of the article.

4. A process of gas plating an article with light metal alloy utilizing scrap light metal alloy as a starting material, said process comprising the steps of admixing said scrap light metal alloy with mercury and heating the mixture to form an amalgam of the light metal alloy, continuing the heating of said amalgam at a higher temperature and under non-oxidizing atmospheric conditions to volatilize the mercury leaving a porous mass of substantially pure light metal alloy while retained in said atmosphere, thereafter reacting the resultant porous metal under said non-oxidizing atmospheric conditions with a reactant to form a heat-decomposable compound of the light metal alloy, and contacting the article to be plated with said heat-decomposable light metal alloy compound while heated to a temperature suflicient to decompose said light metal alloy compound and cause deposition of the light metal alloy onto the surface of the article.

Fischer June 30, 1953 Messner May 3, 1955 

1. A PROCESS OF GAS PLATING AN ARTICLE WITH LIGHT METAL UTILIZING SCRAP LIGHT METAL AS A STARING MATERIAL, SAID PROCKESS COMPRISING THE STEPS SOF ADMIXING SAID SCRIP LIGHT METAL WITH MERCURY AND HEATING THE MIXTURE TO FORM AN AMALGAM OF THE LIGHT METAL, CONTINUING THE HEATING OF SAID AMALGAM AT A HIGER TEMPERATURE AND UNDER NON-OXIDIZING ATMOSPHERIC CONDITIONS TO VOLATILIZE THE MERCURY LEAVING A POROUS MASS OF SUBSTANTIALLY PURE LIGHT METAL WHILE RETAINED IN SAID ATMOSPHERE, THEREAFTER REACTING THE RESULTANT POROUS METAL UNDER SAID NON-OXIDIZING ATMOSPHERIC CONDITIONS WITH A REACTANT TO FORM A HEAT-DECOMPOSABLE COMPOUND OF THE LIGHT METAL, AND CONTACTING THE ARTICLE TO BE PLATED WITH SAID HEAT-DECOMPOSABLE LIGHT METAL COMPOUND WHILE HEATED TO A TEMPERATURE SUFFICIENT TO DECOMPOSED SAID LIGHT METAL COMPOUND AND CAUSE DEPOSITION OF THE LIGHT METAL ONTO THE SURFACE OF THE ARTICLE. 